1. Field of the Invention
The present invention relates to a weight member. In particular, the present invention relates to a weight member for a golf club head.
2. Description of Related Art
A conventional weight member for a golf club head is made by powder metallurgy in which metal powders of high density and high rigidity such as tungsten having a density of 19.30 g/cm3, iron having a density of 7.8 g/cm3, and nickel having a density of 8.9 g/cm3 are pressed and formed and then sintered to form a WFeNi alloy that forms the weight member for a golf club head. Although the powder metallurgy is widely used, several disadvantages exist, including: high cost for molds, low stretchability of products, long processing time, aptness to thermal expansion/shrinkage, and difficulty in forming delicate patterns, letters, serial number, trade names, etc.
Another method for manufacturing a weight member made of WFeNi alloy includes a precision casting process in which a specific metal melting sequence and a specific composition ratio are utilized to prevent sedimentation of tungsten having a high melting point. In the precision casting process, nickel of 30%-50%, iron of 30%-50%, tungsten of 20%-35%, silicon of less than 1%, manganese of less than 1%, and niobium of less than 0.5% are fed into a high-temperature furnace at a temperature above 1450xc2x0 C. and melt to form a weight weight member made of WFeNi alloy for a golf club head. The weight member is then embedded or welded to a golf club head body that is generally made of stainless steel, such as stainless steel of SUS304, 17-4, and 4130 series.
This precision casting process overcomes the problems of the above conventional powder metallurgy. However, as illustrated in FIGS. 1 and 2 of the drawings, if the mixture ratio of the nickel, iron, and tungsten was not properly controlled, a pearlite structure was precipitated in a base of a xcex3 (iron, nickel) phase of the WFeNi alloy, deteriorating the rust-resisting property of the weight member. The upper portion above a horizontal welding line in FIG. 1 of the drawings shows the weight member made of WFeNi alloy, and the lower portion below the horizontal welding line is the base material of the weight member. FIG. 2 is an enlarged view of the pearlite structure. During spray testing at 40xc2x0 C. for 24 hours (which simulates a highly corrosive environment) to the WFeNi alloy by using NaCI solution of 5% by weight, the rusted area of the WFeNi alloy often exceeded 8% of the overall surface area of the WFeNi alloy.
Further, as illustrated in FIG. 3, since tungsten was often precipitated on the surface of the WFeNi alloy (the deep color portion is the pearlite structure and the white portion surrounded by the pearlite structure is the precipitated tungsten), the tungsten/xcex3 (iron, nickel) phase formed by the alloy caused patterns on the weight member made of WFeNi alloy after grinding and polishing procedures. As a result, the appearance of the polished weight member was adversely affected. Further, an obvious insertion line was generated when the weight member made of WFeNi alloy was directly embedded into a bottom surface of a golf club head body. Further, the insertion line of the products varied in response to the thickness ground off, the angle of grinding. Thus, it is difficult to control the processing conditions.
An object of the present invention is to provide a weight member for a golf club head, wherein chromium is added during the precision casting process to prevent the pearlite structure from being precipitated in the xcex3 (iron, nickel) phase of the WFeNi alloy that forms the weight member, thereby improving the rust-resisting property of the weight member.
Another object of the present invention is to provide a weight member for a golf club head, wherein the mixture ratio of nickel to tungsten is controlled during the precision casting process to prevent the pearlite structure from being precipitated in the xcex3 (iron, nickel) phase of the WFeNi alloy that forms the weight member, thereby providing an aesthetically pleasing appearance of the resultant golf club head to which the weight member is directly engaged. The uniformity of the shining finishing, the appearance, and the assembling tolerance of the weight member are improved.
A further object of the present invention is to provide a weight member for a golf club head, wherein silicon is added during the precision casting process to prevent poor flowability of the poured molten metal, thereby improving the efficiency of the process.
Still another object of the present invention is to provide a weight member for a golf club head, wherein manganese, copper, vanadium, and niobium are added during the precision casting process to increase the flowability of the poured molten metal and to assist in removal of gas, thereby improving the mechanical strength of the weight member.
To achieve the aforementioned objects, the present invention provides a weight member for a golf club head that is made of a WFeNi alloy by a precision casting process. The WFeNi alloy includes nickel 30-60 wt %, tungsten 15-30 wt %, chromium 1.5-10.0 wt %, and iron that is the remaining portion. Chromium improves the rust-resisting property of the weight member and lengthens the life of the weight member. Uniformity of shining finishing of the weight member can be improved by controlling a mixture ratio of nickel to tungsten. Silicon may be added to improve the flowability of the molten metal. Manganese, copper, vanadium, and niobium may be added to improve the mechanical properties of the weight member.